Chemical Changes Flashcards
What is the PH scale?
A measure of how acidic or alkaline a solution is
What does it mean when the PH of a solution is low or high?
Low= the more acidic it is
High= the more acidic it is
What has a PH of 7?
A neutral substance (pure water)
How can you measure ph electronically?
pH probe attached to the pH meter
The probe is placed into the solution you are measuring and the pH is given on a digital display as a numerical value.
-more accurate than an indicator
How can you measure the pH of a solution?
-wide range indicator
-pH indicator
What does an acid form?
An acid forms aqueous solutions with a pH of with a pH of less than 7
What ions do acids form in water?
H+ ions
What substance does a base form?
A substance with a pH greater than 7
What is an alkali?
A base that dissolves in water to form a solution with a pH greater than 7
What do alkalis form?
OH- ions in water
What is neutralisation?
The reaction between acids and bases
Neutralisation between acids and alkalis (in terms of H and OH-)
H+ + OH- -> H2O
Neutralisation between acids and bases
Acid + base —> salt + water
What colour is litmus paper in alkali?
Litmus paper is blue in alkalis
What colour is litmus paper in acids?
Litmus paper is red in alkalis
What are titrations used for?
Titrations allow you to find unknown concentration of acids or alkalis
What is the ‘end point’ of a titration?
The end point at which all of the acid or alkali is neutralised, and the indicator changes colour
What colour is phenolphthalein in an acidic solution?
Colourless
What colour is phenolphthalein in a neutral solution?
Colourless
What colour is phenolphthalein in an alkaline solution?
Pink/ red
What colour is methyl orange in an acidic solution?
Red
What colour is methyl orange in an alkaline solution?
Yellow
What is pH?
A measure of the concentration of H+ ions in a solution
What is a strong acid? + examples
An acid which completely ionises in an aqueous solutions (e.g sulfuric, hydrochloric and nitric acids)
What is a weak acid? + examples
Acids that do not fully ionise in an aqueous solution
How does the pH differ between strong and weak acids?
The strong acid will have a lower pH as it it will more fully ionise and so release more H+ ions
What category of acids are weak acids?
Carboxylic acids
Is the ionisation of strong acids reversible?
Is the ionisation of weak acids reversible?
The ionisation of strong acids are not reversible
The ionisation of weak acids are reversible
Why are strong acids more reactive than weak acids?
Strong acids have great concentration of H+ ions, so more of them will react a given amount of time. This will increase the rate of reaction
What is a good indicator to use for a titration between a strong acid and a weak alkali?
Methyl orange
Each time the pH increase by 1, how much does H+ concentration change by?
For each increase by 1 on the pH scale, the concentration of H+ ions gets 10x lower
For each decrease by 1 on the pH scale, the concentration of H+ ions gets 10 x higher
(Remember low pH is acidic- and acidic solutions have a high concentration of H+ ions)
What is the ionic equation for a neutralisation reaction?
H+ + OH- —> H2O
What is the general word equation for the reaction between an acid and a metal oxide?
Acid + metal oxide —> salt + water
What is a general word equation for the reaction between an acid and a metal hydroxide?
Acid + metal hydroxide —> salt + water
What is the general word equation for the reaction between an acid and a metal carbonate?
Acid + metal carbonate —> salt + water + carbon dioxide
What is the general word equation for the reaction between an acid and a metal?
Acid + metal —> salt + hydrogen
What are the acid rules? (Writing equations)
Hydrochloric acid = chloride salts
Phosphoric acid= phosphate salts
Nitric acid= nitrate salts
Sulphuric acid= sulfate salts
What are the steps for obtaining soluable crystals from an acid-base reaction?
(Required practical)
- Place dilute acid in a beaker and gently heat it
- Add the solid base bit by bit until it stops reacting, which means it’s in excess
- Isolate the salt solution by filtering out the excess solid base using filter paper and a funnel
- Heat the salt solution gently in water bath until crystals start to form
- Let the solution cool further, which will cause more crystals to precipitate
- Filter out the soluble salt crystals using filter paper and a funnel
What is the effect of using reactants with increased reactivity in a reaction?
Increased reactivity means the reaction will take place more quickly, or more vigorously
How can you investigate the reactivity of a metal using an acid?
Acid + metal —> salt + hydrogen
- Firstly react the metal with an acid
- When the metal reacts, bubbles of hydrogen will be released
- The faster the bubbles are produced, the faster the reaction is, and so the more reactive the metal must be
How can you investigate the reactivity of metals using temperature change?
More reactive metals will lead to larger temperatures changes
- Reactive each of the metals with either water or acid over a set period of time
- Ensure that the surface area of the mass of the metal is the same each time
- Measure the rise in temperature
- The greater the temp change, the more reactive the metal must be
Why can it be dangerous to react very reactive metals with acids or water?
Very reactive metals can be explosive and produce many bubbles
Which metals don’t react with water?
Less reactive metals such as zinc, iron and coppee
In a displacement reactions, which ions are reduced?
Metal ions are reduced- this means they gain electrons
Will acids react more vigorously with hot or cold water?
Hot water, the higher temps results in a faster rate of reaction
Would powered metal, or a single chunk (both the same mass) react more vigorously?
Powdered metal, as it would have a larger surface area
What is an oxidation reaction (in terms of oxygen)?
An oxidation reaction refers to a substance reacting with oxygen
E.g copper is oxidised to form copper oxide
What is a reduction reaction (in terms of oxygen?)
A reduction reaction refers to a substance losing oxygen.
For example, copper oxide is reduced to form copper
When mined from the ground, what form are metals normally found in? And what is it called?
They are usually bonded to other elements, most often oxygen
We usually refer to these oxidised metals as ‘ores’
E.g iron oxide may be called ‘iron ore’ and copper oxide may be called ‘copper ore’
What are two ways that metals can be extracted from their ores ?
- Reduction with carbon
- Electrolysis
Which metals can be reduced with carbon?
Only metals that are less reaction than carbon:
1. Zinc
2. Iron
3. Copper
Describe how metal ores can be reduced using carbon.
- React the metal ores with carbon
- Carbon will displace the metal as it is more reactive
What is the balanced symbol equation for the reduction of FeO with carbon?
2FeO + C —> 2Fe + CO2
Why do some metals not require extraction?
Some metals are so un reactive that they exist in the earth as pure metals (not bonded to any other element)
For example, gold is found as pure gold
What is oxidation (in terms of electrons)?
Oxidation is the loss of electrons
What is reduction (in terms of electrons)?
Reduction is the gain of electrons
What is a redox reaction?
A redox reaction is a reaction in which both oxidation and reduction take place.
What is a useful phrase to remember oxidation and reduction?
OIL RIG
oxidation is loss (of electrons)
Reduction is gain (of electrons)
What is metal displacement?
Metal displacement is where a more reactive metal displaces a less reactive metal in a compound
What is a half equation?
A half equation is an equation that shows the gain or loss of electrons of a single element in a reaction
What is the half equation for the oxidation of magnesium?
Mg —> Mg2+ + 2e-
In a displacement reaction, are the metal ions reduced or oxidised?
The metal ions are reduced (they gain electrons)
In a displacement reaction are the metal atoms reduced or oxidised?
The metal atoms are oxidised (they lose electrons)
Describe what is shown in ionic equations.
In ionic equations, only the particles that react and the products they form are shown- the ions that don’t change are ignored
What do we call ions that aren’t involved in a chemical reaction?
Spectator ions
What is the ionic equation for this reaction: Mg + ZnCl2 —> MgCl2 + Zn
The chloride ions don’t take part in the reaction so they can be removed
So the equation is: Mg + Zn2+ —> Mg2+ + Zn
